Carburetion devices for internal combustion engine

ABSTRACT

The device has a main jet for normal operation and an idling circuit, both opening into the intake pipe and provided with calibrated orifices to adjust the richness of the air/fuel mixture. An adjustable throttle enables the idling mixture to be adjusted. The adjustable throttle can be bypassed through a passage to the mixing channel during deceleration. The passage has a closing member actuated by a capsule governed by the suction in the intake and by a member sensitive to the engine&#39;&#39;s speed. When the bypass is closed the capsule is connected to atmospheric pressure. The capsule is fixed to an element compensating for altitude.

1 51 July 18,1972

United States Patent Pierlot .26l/DIG. l9 .......261/DlG. l9 ...26l/DlG. l9 ........26l/39 A ........261/39 A ...26l/DlG. l9 ....26l/DIG. 19

mm m n "t" u. "e" mm ws m m e. 1.. mmmm a b mmoim Cc MMs 9 85387 5634466 9999999 1111111 ywwuyu 11 1 85790094 986 m02 9 3 .3 7349843 7938 65 ,9 ,5 ,3 2222233 Primary Examiner-Tim R. Miles Attorney-Fleit, Gipple & Jacobson [57] ABSTRACT The device has a main jet for normal operation and an idling circuit, both opening into the intake pipe and provided with calibrated orifices to adjust the richness of the air/fuel mixture. An adjustable throttle enables the idling mixture to be adjusted. The adjustable throttle can be bypassed through a passage to the mixing channel during deceleration. The passage has a closing member actuated by a capsule governed by the suction in the intake and by a member sensitive to the engine's speed. When the bypass is closed the capsule is connected to atmospheric pressure. The capsule is fixed to an element compensating for altitude.

6 Claim, 5 Drawing Figures .261/23 A, 123/97 B, 26l/DIG. 19, 261/41 D, 261/69 R, 261/39 A Feb. 26, 1970 References C [22] Filed:

[2l] Appl. No.:

[30] Foreign Application Priority Data March 3, 1969 Sept. 30, 1969 France.....

[51] Int. Cl.

[58] Field ofSearch..............

Patented July 18, 1972 3 Sheets-Sheet 2 Patented July 18, 1972 3 Shoots-Shut 3 CARBURETION DEVICES FOR INTERNAL COMBUSTION ENGINE The present invention relates to improvements in carburetion devices for internal combusion engines. More particularly it relates to carburetion devices, for internal combustion engines of automobile vehicles, of the type of those which comprise two separate supply circuits for fuel generally mixed with air, namely a main nozzle or jet circuit for normal operation and an idling circuit opening into the intake pipe downstream of the main throttle member actuated by the driver (at least when this member is closed). These devices include also, generally, a supply circuit called a progress" or transfer circuit opening into the intake pipe through at least one transfer orifice located so as to pass from upstream to downstream of the main throttle member when the latter opens slightly.

It is known that, during decelerations of the vehicle, that is to say during periods where the main throttle member occupies its minimal open position and where the engine is driven by the vehicle at a relatively high speed and in any case greater than that of idling, there is generally advantage in sending to the engine an amount of air/fuel mixture greater than that which would be sent by the same carburetion device on idling.

It has already been proposed, to this end, to provide means adapted to slightly open the main throttle member on decelerations. But these means are rather difficult to produce and their operation is very delicate since a slight variation of the slightly open position can change notably the flow and/or the richness of the mixture thus obtained. In fact, the slight opening of the throttle member generally places the edge of the latter over the transfer of orifices and the adjustment of the flow of these orifices is very delicate and necessitates a well determined position of the edge of the throttle member.

It is for this reason that it was thought preferable to send to the carburetion device, during periods of deceleration, an excess of air/fuel mixture to the engine while leaving the main throttle member in its idling position.

Moreover, it is necessary that the richness of the air/fuel mixture produced during the idling of the engine and that of the mixture produced during periods of deceleration be practically the same although the flows of this mixture must be distinctly different. In order that these richnesses correspond well to the emission of exhaust gases which are the least noxious, they should be adjusted once and for all by the constructor in the workshop and the user should not have the possibility of modifying them.

For this purpose, it has been proposed, in British Pat, application, No. 17,607/69 that the idling circuit include at least one air intake channel and one fuel supply channel provided respectively with calibrated orifices adapted to adjust the richness of the idling mixture as well as a mixture channel at which the two preceding channels terminate, which mixture channel is provided with an adjustable throttle enabling the user to adjust the flow of the air/fuel mixture on idling and to which is connected a passage by-passing the said throttle adjustable and adapted to be opened automatically on periods of deceleration.

According to this patent application, the obturating member of the by-pass passage was actuated by a suction sensitive means adapted to be connected to the zone of the supply pipe situated downstream of its main member through an electromagnetic valve controlled by an electronic device sensitive to the speed of the engine or, at least, of the vehicle driven by this engine. The assembly was such that the by-pass passage was only freed through its closing member when, simultaneously, the electronic device recorded a high speed and the suction sensitive means a strong suction which corresponds to the closing of the main throttle member.

This solution, whose operation is satisfactory, presents however the drawback of being rather costly since the assembly of the electromagnetic valve and of its electronic device is of relatively complicated construction and of rather high cost rice. p It is an object of the present invention to overcome this drawback.

Other objects of advantages'will emerge from the description which follows.

According to the invention, there is provided a carburetion device of which the idling circuit comprises not only a mixture channel at which an air supply channel and a fuel supply channel terminate, provided respectively with calibrated orifices adapted to adjust the richness of the air/fuel mixture, and which is provided with an adjustable throttle enabling the user to adjust the flow of the mixture which is delivered on idling through this mixture channel through an orifice opening into the zone of the intake pipe situated downstream of its main throttle member (at least when this member is closed) but also a passage connected to the mixture channel so as to bypass said adjustable throttle and adapted to be freed, during periods of deceleration, by a closing member which is actuated by a first suction sensitive means sensitive to the suction existing in the said zone which is transmitted to it through a member sensitive to the engine speed, which carburetion device is characterized by the fact that this latter member is constituted by a second suction sensitive means sensitive to the suction existing at one point of the intake pipe located so as to pass from downstream to upstream of the main throttle member when the latter is slightly opened, first suction sensitive means being arranged to be subjected to atmospheric pressure when said closure member isolates the bypass passage.

The replacement of said assembly with an electromagnetic valve and of its electronic device by a single suction sensitive means, generally with a diaphragm, constitutes a genuine economy. In spite of this, the operation remains satisfactory. In fact, the second suction sensitive means may be rendered sensitive to a slight difference of suction, because the travel of its movable or deformable element, such as a diaphragm, can be held very slight. On the other hand, the first suction sensitive means being subjected suddenly to a considerable difference of pressure (between atmospheric pressure and the suction existing in the above-said zone), the travel of its movable element can be sufficiently great to cause complete opening of the closure member which it controls.

Preferably, the carburetion device thus defined is also characterized by the fact that the second suction sensitive means is constituted by a capsule, with an inner spring, housed in a chamber connected to the above-said zone.

Such a carburetion device operates correctly for a rather restricted altitude limit, but if it is adjusted to operate at sea level for example, it no longer operates correctly on arriving at altitudes comprised between 1,000 and 2,000 meters, since the device then delivers permanently through the by-pass passage held open, which is manifested by an excessive idling speed and incompatible with comfort in the use of the vehicle whose engine is supplied through the device concerned.

To overcome this latter drawback, the carburetion device can also be characterized by the fact that the above-said capsule anchored on an element adapted to be displaced as a function of the difference between atmospheric pressure and the pressure existing in the above-said zone, so that, the lower the atmospheric pressure, that is to say the higher the altitude, the lower must be the pressure existing in this zone for it to be transmitted to the first suction sensitive means.

In order that the invention may be more fully understood, several preferred embodiments of a carburetion device according to the invention are described below, purely by way of illustrative but non-limiting examples, with reference to the accompanying drawings in which:

FIG. 1, shows in vertical diagrammatic section, a first embodiment of a carburetion device constructed according to the invention;

FIG.) shows a variation of a portion of the embodiment shown in FIG. 1;

FIG. 3 shows, in diagrammatic vertical section, a second embodiment of a carburetion device according to the invention;

FIG. 4 shows curves illustrating the operation of the embodiment of FIG. 3; and

FIG. shows a third embodiment which is a multiple carburetion device.

In order to establish a earburetion device of an internal combustion engine, more particularly for vehicle engines, one proceeds in the following or similar manner.

As regards firstly the carburetion device as a whole, this is established in any suitable manner such that it comprises as shown in FIGS. 1 to 3:

a supply pipe 1 connected to the intake pipe of the engine, this pipe possessing an air inlet 2 and a main throttle member (or butterfly valve) 3 actuated by the driver;

a main jet circuit for normal operations;

an idling orifice 4 opening into the pipe I, downstream of the main throttle member 3, at least when this member is closed;

-- and at least one and for example two transfer orifices S situated in said pipe 1 so as to pass from upstream to downstream of the main throttle member 3 when the latter is displaced from the closure position shown.

As regards the main jet circuit (not shown), this is constituted by a channel, supplied with fuel by a constant level tank, which opens into the pipe 1 at the level of a venturi 6 through orifices not shown.

There is supplied, on one hand, the idling orifice 4 and, on the other hand, the transfer orifices 5 through separate and distinct circuits of the main jet circuit, which separate circuits comprise each a calibrated orifice 7 or 8 for the metering of the fuel and at least one calibrated orifice 9 or 10 for the quantity control of the air, these orifices 7 to 10 serving to determine the richness of the mixtures delivered respectively through the two circuits concerned. The fuel of one or other of these separate circuits is raised into the above-said tank, through a channel 11 as regards the idling circuit.

The calibrated orifice 7 opens into a mixture channel 12 of which the upper part communicates with the pipe 1 through the calibrated orifice 9 and which, at its lower part, opens into the pipe 1 by means of the orifice 4.

The second circuit comprises a descending channel 13 which communicates, at its upper part, with the air intake 2 by means of the calibrated orifice 10 and of which the lower portion opens into the pipe through the orifices 5.

The channel 13 of the transfer circuit is advantageously made to communicate with the pipe I, not only through the one or more transfer orifices 5, but also through an orifice 14 opening constantly downstream of the throttle member 3. This orifice may be provided with adjusting means, such as a screw 15. The orifice 14 has the effect of maintaining the fuel in the transfer channel 13 during idling operation.

The channel 12 is provided with an adustable throttle, constituted generally by an orifice 16 in which may be displaced the end of a screw 17 immobilized, for example, by a spring 18, and there is connected onto the channel 12 a passage 19 by-passing the said adjustable throttle 16, 17 and adapted to be opened automatically on periods of decelaration. periods It is known that the conditions of deceleration of the engine, on the one hand, have in common with idling conditions the closing of the throttle member 3 but are distinguished from the latter by an engine speed greater than a given limit and, on the other hand, have in common with the normal operating conditions, a speed greater than the said limit but being distinguished from the latter by the closure of the main throttle member. This closure may be evaluated indirectly by the suction existing in a suitably chosen zone of the pipe I.

To produce the automatic closing and opening of the passage 19, recourse is therefore had to sensing means not only to the position of the main throttle member 3, but also to the engine speed evaluated itself also by the suction existing in the pipe I downstream of the throttle member 3.

There is made to pass through by the passage 19 a chamber 20 bounded by a diaphragm 21 and provided with an orifice 22 forming the donwstream portion of the passage 19. The diaphragm 21 bears a needle 23 which cooperates with the orifice 22 and it limits, on the opposite side to the chamber 20,

a second chamber 24 which can communicate through the assembly of two channels 25 and 26 with a zone of the pipe 1 situated so as to pass from downstream to upstream of the throttle member 3 when the latter is slightly opened. The necdle 23 is urged to closure by a spring 27 and can be opened by the action of the suction which is exerted in the chamber 24 when, at the same time, the throttle member 3 is closed (channel 26 downstream of this member) and a valve 28, acting between the channels 25 and 26, is opened by a second suction sensitive member, when the engine speed is greater than the above-said limit (1,300 to 1,400 turns/minute, for example). The chamber 24 can be connected permanently to the atmosphere, through an orifice 29 of slight cross-section, which opens for example into the pipe 1 upstream of the throttle member 3, and possibly also (as shown) through the channel 25; the permanent connection of the chamber 24 with the atmosphere could also be effected by means of the portion of the channel 12 situated upstream of the orifice 7.

To constitute the second suction sensitive means, the channel 25 may be terminated in a closed chamber 30, according to the embodiment of FIG. 1, by a diaphragm 31 of which the movable mechanism bears the valve 28. This valve cooperates with a seating 32 and, according to whether it is on this seat or not, the communication between the channel 25 and the chamber 30 is cut or established. This chamber communicates in addition through the channel 26 with the intake pipe 1 downstream of the throttle member 3, in the immediate proximity of the edge of the latter, at least when this member occupies its idling position.

A spring 33 acts on the diaphragm 31 (towards the right of FIG. 1 to maintain the valve 28 on its seating 32 as long as the suction existing in the pipe 1 downstream of the throttle member 3 is equal or less than the suction exisiting on idling.

On the opposite side to the volume 30 with respect to the diaphragm 31, there occurs a closure cover 34 in which is mounted an adjusting screw 35 acting on a spring 36 and capable of being locked for example by a check nut 37. This device serves, by acting on the screw 35, to adjust, due to the spring 36, the exact tension of the spring 33 so that the latter yields as soon as the suction in the chamber 30 exceeds the value existing on idling. The cover 34 is pierced by a hole 38 adapted to subject the other surface of the diaphragm 3] to atmospheric pressure.

The operation of the device is as follows.

An idling speed is established so that the throttle member 3 is almost completely closed and the orifice 14 extremely small. In this way, the mixture supplied to the engine, to turn it at idling speed, is very nearly exclusively supplied through the channel 12 of which the section of the passage towards the pipe 1 is adjusted finally by the screw 17 acting through its cone in the orifice 16. In fact, on idling, the suction existing in the pipe 1 at the outlet of the channel 26 is relatively slight, so that the spring 33 is preponderent and maintains the diaphragm 31 towards the right of FIG. 1, which has the effect of closing the valve 28 and of thus interrupting communication between the channel 26 and the chamber 24. The spring 27 holds the diaphragm 21 towards the right of FIG. 1, which ensures the closing of the orifice 22 by the needle 23. This is facilitated by a very slight intake of air into the chamber 24 through the orifice 29.

It will be understood that this idling device gives a practically constant richness, whatever its delivery.

Consequently, if the orifices 7 and 9 are predetermined in workshop, the user has only at his disposal the screw 17 which enables him to vary the free cross-section of the orifice l6 and, consequently, to modify the idling speed without however modifying the richness of the mixture sent to the engine.

On a deceleration, the throttle member 3 occurs again in the same position as on idling, but the suction in the pipe 1, downstream of the throttle member 3, increases beyond the suction existing on idling and, by acting on the diaphragm 31, causes compression of the spring 33 and a displacement of small amplitude of the diaphragm 31 towards the lift of FIG. 1,

a displacement sufficient however to open the seating 32 normally closed by the valve 28. The above-said suction is transmitted then through the channels 26 and up to the chamber 24 where it is substituted for the atmospheric pressure. This causes a displacement of large amplitude of the diaphragm 21 and the needle 23 is thus disengaged freely from the orifice 22 (as shown in FIG. 1). Mixture emerging from the channel 12 passes through the passage 19 and the chamber 20 towards the orifice 22, this mixture being added to that which is delivered through the orifice 4.

As has been seen, the richness of the mixture thus introduced into the engine is substantially the same on idling and in the course of decelerations, but the delivery is greater on decelerations, which favors combustion and reduces the level of pollutants in the exhaust gases.

When the vehicle driven by the engine descends a slope at constant speed with the throttle member 3 slightly opened, the engine can turn at high speed and the suction existing in the pipe 1, downstream of the said member 3, is practically as high as under the conditions of deceleration. However, as the channel 26 opens then upstream of the throttle member 3 and occurs thus at a pressure substantially equal to atmospheric pressure, the seating 32 and consequently the orifice 22 are closed respectively by the valve 28 and the needle 23 and the mixture is hence only delivered through the idling and progression orifices 4, 5. Finally, the increase in flow through the passage 19 can only be effected under the double condition that the throttle member 3 is closed to the maximum and that the engine speed is sufficient to cause opening of the valve 28.

This solution is particularly advantageous in the case of a carburetion device composed of several elemental carburetors, since, at this time, the flow variation device can be the same for all the elemental carburetors.

In this case, the common orifice 22 opens, not into one of the elemental carburetors, but into a tube 45 (FIG. 5) which makes the supply pipes communicate between thesmselves such as 1 of the various carburetors, downstream of their respective throttle members such as 3.

The main advantage of this device is to give rise, on each deceleration, to strictly one position of the throttle member 3 which comes to rest on its stop usually provided (not shown in the FIGS.), which enables strict adjustment of the air which can pass around this throttle member and especially strict positioning of this member with respect to the transfer orifices 5 which normally occur at this moment upstream of the throttle member 3. Consequently, the latter do not participate in the supply of the engine, which would be the case if, as in most known constructions, the throttle member 3 was slightly open (from the idling position) during periods of deceleration.

Since the surface of the diaphragm 31 opposite the chamber 30 is subjected to atmospheric pressure, the operation of the device of FIG. 1 is only certain on condition that the atmospheric pressure does not vary too much; in particular, when the altitude increases, operation becomes defective. It is known, in fact, that, on idling, the pressure which exists in the pipe 1, downstream of the throttle member 3, has an absolute value almost constant for a fixed altitude. Since the diaphragm is subjected to the difference between the absolute external pressure barometric pressure) and the absolute internal pressure (chamber 30), its operation varies with the barometric pressure since the internal pressure remains practically constant.

The embodiment of FIG. 2 overcomes this drawback by substituting for the diaphragm 31 a capsule 39, generally empty, whichan inner spring tends to hold at a certain length. This capsule is housed inside the chamber 30 and is coupled to the valve 28. The axial position of the capsule may be adjusted by means of a screw 35a which is locked on the cover 340 of the chamber 30 by means of a lock-nut 37a.

The assembly of FIG. 2 operates like that of FIG. 1, the capsule 39 elongating under the effect of the suction existing in the pipe 1 and transmitted through the channel 26, but with this difference that its elongation and the point where it starts to operate depends little on the ambient atmospheric pressure.

The embodiment of FIG. 2 is consequently fool proof, for moderate variations of atmospheric pressure. On the other hand, when the altitude increases, the value of the absolute pressure in the pipe 1, downstream of the throttle member 3, changes a little due to the fact that the exhaust of the engine is effected in a medium at lower barometric pressure, which slightly modifies the intake pressure in the pipe I. The embodiment of FIG. 3 has the object of eliminating this influence of altitude.

Although, in the embodiment of FIG. 2, the capsule is anchored on a rigid and fixed part constituted by the cover 34a of the chamber 30, in the embodiment of FIG. 3, which is apart from this identical with that of FIG. 2, the capsule 39 is anchored on a rigid part 40 which is movable as a function of the difference between the atmospheric pressure and the pressure existing in the zone of the pipe 1 situated downstream of the main throttle member 3, so that, the lower the atmospheric pressure, that is to say the higher the altitude, the lower must be the pressure existing in this zone for it to be transmitted to the first suction sensitive means, that is to say to the chamber 24.

To this end, the part 40, which is traversed by the screw 35a with the interposition of a sealing joint 41, is fixed in sealed manner to an element 42 adapted to be displaced or deformed with respect to the casing 43 which bounds the chamber 30 and of which it forms the sealed bottom. The element 42 is preferably constituted by a metallic bellows welded through an annular edge 42a to the element 40 and through another annular edge 42b to the casing 43. In this way, the inner surface of the bellows is subjected to the pressure of the chamber 30 and its outer surface to atmospheric pressure.

In this way, if variations in pressure P-P, exist (P being the atmospheric pressure and P, the absolute pressure which exists in the pipe 1 downstream of the main throttle member 3), the bellows 42 is deformed by displacing the part 40 and, consequently, the tail 35a of the capsule 39 parallel to the axis of this latter. This movement is added to the movement itself of the capsule 39 and it is then the resultant of the two movements which actuate the opening of the valve 28 and in consequence the introduction of an additional mixture of air and of fuel through the orifice 22.

This operation is illustrated by the curves of FIG. 4 where the altitude H is shown as abscissa (expressed in meters and the absolute pressure p as ordinate. The absolute pressure existing in the pipe 1 during periods of deceleration is shown by the curve A However, when the speed of the engine diminishes, this absolute pressure increases and reaches a value for which the needle 23 must be closed. This value is shown by the curve A,. As for idling properly so called, its curve corresponds to absolute pressures in the pipe 1, which have values still higher and which have not been shown in FIG. 4. In the course of deceleration, the opening of the valve 28 then its closure must intervene for absolute pressures comprised between the curves A, and A It is seen that, up to 1,000 meters of altitude, these two curves are substantially parallel and indicate a practically constant absolute pressure. It is only beyond 1,000 meters that the absolute pressures decrease and this at a rate much less rapid than the atmospheric pressure.

In the embodiment of FIG. 2, the capsule 39 is adjusted so that the valve 28 is opened in the course of deceleration for a value of the absolute pressure equal to B and is closed for a value of this pressure equal to B,.

In the absence of the corrective device according to the embodiment of FIG. 3, the curves B, and B are horizontal. It is seen therefore that at around 1,400 meters altitude, the curve B, intersecting the curve A,, the device commences to no longer operate since the valve 28 is not closed when the curve A, is reached. For altitudes of about 2,000 meters, the needle 23 will hence always remain open, even on idling of the engine, thereby causing idling speeds distinctly too high.

Due to the corrective means illustrated in FIG. 3, when the suction existing in the pipe 1 downstream of the throttle member 3 is transmitted through the channel 26 to the chamber 30, there is observed not only an elongation of the capsule 39 under the effect of this suction, but also a displacement, towards the lift of FIG. 3, of the part 40 under the effect of the difference of pressure P-P,.

For sea level, the capsule 39 is adjusted by means of the lock-nut 37a to operate at absolute pressures b and b along the origin of.curves B, and B taking into account the displacement of the bellows 42.

When the altitude increases, the pressure P diminishes much more quickly than the pressure P,, the difference P-P becomes less important and, consequently, the displacement of the part 40 by deformation of the bellows 42 becomes more slight so that a lower absolute pressure is necessary in the chamber 30 to make the valve 28 operate.

If the deformations of the bellows 42 are determined in consequence, the points of opening and of closing of the valve 28 are displaced along curves C, and C (FIG. 4) parallel to the curves A and A Consequently, the device operates whatever the altitude and enables a suitable idling speed to be reestablished whatever the value of the atmospheric pressure, at least for altitudes normally attainable by terrestrial vehicles.

As goes without saying, and as emerges already besides for the preceding description, the invention is in no way limited to that of its methods of application, nor to its methods of production of its various parts, which have been more particularly described; it embraces, on the contrary, all variations, especially that where the bellows 42 of FIG. 3 would be replaced by any diaphragm, but the metallic bellows seems more advantageous due to the fact of its relative rigidity, since it enables a fixed point to be constituted for the capsule 39 on which can be clamped the lock-nut 37a to ensure the initial adjustment of the capsule.

lclaim:

l. Carburetion device comprising two separate supply circuits for fuel generally mixed with air, namely a main jet circuit for normal operation and an idling circuit both opening into the intake pipe of the device, which idling circuit comprises a mixing channel at which an air supply channel and a fuel supply channel terminate, provided respectively with calibrated orifices adapted to adjust the richness of the air/fuel mixture, and which is provided with an adjustable throttle enabling the user to adjust the flow of mixture which is sucked on idling through said mixing channel by means of an orifice opening into the zone of the intake pipe situated downstream of its main throttle member actuated by the driver, at least when said throttle member is closed, and a bypass passage connected to the mixing channel so as to bypass said adjustable throttle and adapted to be freed, during periods of deceleration, by a closing member which is actuated by a first suction sensitive means sensitive to the suction existing in said zone which is transmitted to it through a member sensitive to the speed of the engine, said speed-sensitive member being constituted by a second suction sensitive means sensitive to the suction existing at a point of the intake pipe situated so as to pass from down-stream to upstream of the main throttle member when the latter is slightly opened, said first suction sensitive means being arranged to be subjected to atmospheric pressure when said closing member isolates said bypass passage and said second suction sensitive means being constituted by a capsule containing a spring, said capsule being housed in a chamber connected to said point of the intake pipe.

2. Carburetion device according to claim 1, wherein a variable volume chamber of said first suction sensitive means communicates permanently, through an orifice of small section, with a zone in which exists a pressure substantially equal to atmospheric pressure.

3. Carburetion device according to claim 1, wherein said capsule is anchored on an element adapted to be displaced as a function of the difference between atmospheric pressure and the pressure existing at said point of the intake pipe, so that the lower the atmospheric pressure the lower must be the pressure existing at said point for it to be transmitted to the first suction sensitive means.

4. Carburetion device according to claim 3, including a casing bounding said chamber, an element adapted to be spacially modified with respect to said casing and of which it forms the sealed bottom, said element being constituted by a rigid part to which said capsule is fixed by screwing.

5. Carburetion device according to claim 4, wherein said element is constituted by a metallic bellows.

6. Multiple carburetion device, constituted by the combination of at least two single carburetion devices according to claim 1, and including a single bypass passage opening into a tube uniting the intake pipes of the single carburetion devices, downstream of their respective main throttle members. 

1. Carburetion device comprising two separate supply circuits for fuel generally mixed with air, namely a main jet circuit for normal operation and an idling circuit both opening into the intake pipe of the device, which idling circuit comprises a mixing channel at which an air supply channel and a fuel supply channel terminate, provided respectively with calibrated orifices adapted to adjust the richness of the air/fuel mixture, and which is provided with an adjustable throttle enabling the user to adjust the flow of mixture which is sucked on idling through said mixing channel by means of an orifice opening into the zone of the intake pipe situated downstream of its main throttle member actuated by the driver, at least when said throttle member is closed, and a bypass passage connected to the mixing channel so as to bypass said adjustable throttle and adapted to be freed, during periods of deceleration, by a closing member which is actuated by a first suction sensitive means sensitive to the suction existing in said zone which is transmitted to it through a member sensitive to the speed of the engine, said speedsensitive member being constituted by a second suction sensitive means sensitive to the suction existing at a point of the intake pipe situated so as to pass from down-stream to upstream of the main throttle member when the latter is slightly opened, said first suction sensitive means being arranged to be subjected to atmospheric pressure when said closing member isolates said bypass passage and said second suction sensitive means being constituted by a capsule containing a spring, said capsule being housed in a chamber connected to said point of the intake pipe.
 2. Carburetion device according to claim 1, wherein a variable volume chamber of said first suction sensitive means communicates permanently, through an orifice of small section, with a zone in which exists a pressure substantially equal to atmospheric pressure.
 3. Carburetion device according to claim 1, wherein said capsule is anchored on an element adapted to be displaced as a function of the difference between atmospheric pressure and the pressure existing at said point of the intake pipe, so that the lower the atmospheric pressure the lower must be the pressure existing at said point for it to be transmitted to the first suction sensitive means.
 4. Carburetion device according to claim 3, including a casing bounding said chamber, an element adapted to be spacially modified with respect to said casing and of which it forms the sealed bottom, said element being constituted by a rigid part to which said capsule is fixed by screwing.
 5. Carburetion device according to claim 4, wherein said element is constituted by a metallic bellows.
 6. Multiple carburetion device, constituted by the combiNation of at least two single carburetion devices according to claim 1, and including a single bypass passage opening into a tube uniting the intake pipes of the single carburetion devices, downstream of their respective main throttle members. 